1. Field of the Invention
This invention relates to torque measurement in a mechanical device such as a gear speed reducer by sensing the tangential force of the gears transmitted to one of the rotating members.
2. Description of the Prior Art
All rotating machines such as motors, generators, turbines and mechanical gear trains or transmissions have one major function in common; they produce or transmit torque. They all also absorb some torque which becomes a power loss to the overall system. The method and apparatus for sensing and measuring the torque output power and loss have been a continuous challenge to the engineers in the related field. Most methods for measuring the torque require a modification of the drive train at some point and a device inserted into it or fastened on it to measure torque, such as that described in U.S. Pat. No. 2,359,125. The device described in that patent utilizes strain gages for both the thrust and torque measurement.
Another method measuring torque shown in U.S. Pat. No. 3,595,074 consists of a pair of axially spaced plates having a plurality of flexure plates mounted therebetween wherein one plate is attached to a rotary machine housing and the other plate to the drive mechanism. The drive mechanism is supported by this torque transducer from the housing surface and is mounted in cantilever fashion at the unsupported ends of the flexure plates. The reaction or countertorque between the mounting plates, in proportion to the input or output torque, and the relative movement of one plate with respect to the other plate, is measured and hence the torque determined by use of a differential transformer, which develops an electrical signal proportional to the angle through which the end plate is rotated.
In still another U.S. Pat. No. 3,745,819, the axial thrust developed by tapered roller bearings in response to radial loads exerted on the rotating member is fed through a piston adapted to move axially against a pressure chamber to provide a pressure reading proportional to the radial load imposed on the rotatable member. This device required an additional pressurized and sealed mechanism inside the housing or attached directly to it which has many components in it and is very expensive to manufacture. Other U.S. patents, such as U.S. Pat. No. 2,957,343 shows still another method for measuring torque as a function of thrust using air pressure and in U.S. Pat. No. 1,998,450 the thrust is measured by deflecting a spring which move the plates of an electrical condenser causing a change in the capacitance which is proportional to the axial movement of a shaft. Still other methods employ slip rings and require cutting the shaft and inserting the transducer into the shaft member itself to measure the torque of that shaft. Still another method commercially available employs a Linear Variable Differential Transformer (LVDT) wherein the core position moves as a function of the shaft thrust and hence torque output of the device. Such a unit, however, is very large and requires an extensive modification of the power device.
My invention inserts a transducer into the housing which supports the shaft bearing and senses the tangential force of a rotational member. This approach is a much simpler and more compact package than previous methods and apparatus. As discussed, many methods have been used to detect the rotary motion, separating force, tangential force or axial thrust of a shaft and translate this to the torque developed by the shaft. Although some of the aforementioned patents and methods were used in conjunction with gear trains and power transmissions, none of these solved the problem of measuring the torque in a gear box in the unique way as does my invention.
A gear box and, for that matter, other power transmission systems, usually operate with a continuous bath of oil available to the gears when in use. This lubrication is necessary for translating the high speed and low torque input associated with such devices into a low speed and high torque output. Such units are designed to be as small and compact as possible. A device to measure output torque therefore, must also be small and compact in size to fit into an existing housing or space, be low in cost and capable of constant immersion in oil or other fluids, operate at varying temperatures and contaminated environments, and have a method of remote readout. This remote requirement is necessary in many applications of power transmission and gear reducers since a visual inspection during operation of the assembly itself is not always possible because of its location. Also in gear devices, as well as other machinery, bearings and shafts must maintain their position very accurately under all conditions of operation to assure proper load of the power transmitting parts to maintain minimum deflections and movements often to less than 0.001 inches. This requirement is easily met with my invention.